King, an independent and former two-term governor, is a popular politician among Maine voters. But can his nod for Cutler have any effect in moving voters to Cutler’s camp? Do any endorsements, for that matter, have an impact on the number of votes that are ultimately cast for a candidate?

In short, it depends — on the race, the voter and the entity making the endorsement.

Oprah and Obama

In 2007, internationally known talk show host Oprah Winfrey announced her support for then-Sen. Barack Obama in the Democratic presidential primary between Obama and then-Sen. Hillary Clinton. It was the first time Winfrey — who built a media empire and brand around her talk show, a magazine, a book club and more — publicly endorsed a political candidate.

“I think that my value to him, my support of him, is probably worth more than any check,” Winfrey said on CNN’s Larry King Live.

Obama, of course, went on to defeat Clinton in the primary. But did Winfrey’s support persuade voters to cast their votes for Obama and Clinton?

In a 2012 paper, the researchers from Northwestern University’s Kellogg School of Management and the University of Maryland calculated that Winfrey’s endorsement was worth more than 1 million votes to Obama, enough to propel him to victory. They arrived at their estimate by judging the inclination of “O, the Oprah Magazine” subscribers, who are mostly women, to support Clinton or Obama before Winfrey’s endorsement and the eventual votes they cast.

Rock stars, politicians, interest groups and media

But not every endorsement comes from Oprah or someone of her stature, and not every race is the 2008 Democratic presidential primary. Determining the value of a political endorsement isn’t as simple as judging the impact of Oprah’s endorsement and working backward to adjust for less fame and lower profile races.

The limited political science research available on the impact of endorsements points to a larger impact in races that aren’t top of mind for voters. For example, a 2011 paper by University of Georgia political scientists Richard Vining and Teena Wilhelm concluded that a sitting governor’s decision to endorse in a judicial election — in the 38 states where, unlike in Maine, voters elect their judges — has a big impact on the electoral outcome because of the governor’s high profile in state politics.

“When individuals have little information, as is often the case in judicial elections, they rely on cues and information shortcuts to construct their preferences,” Vining and Wilhelm write. Endorsements from high-profile political figures, interest groups or media organizations can serve as those information shortcuts, sending a signal to voters about a candidate so they don’t actually need to perform their own research.

But endorsements’ effects aren’t always positive. Voters absorb endorsements just as they would any other piece of information they might consider when making a political decision. And that means a partisan bias and desire to reaffirm that worldview colors their interpretation, researchers Kyle Dropp and Christopher Warshaw point out in a 2011 paper analyzing the effect of newspaper endorsements.

As a result, endorsements are more likely to have a positive effect among voters whose ideology lines up more closely with that of the source of the endorsement. Similarly, voters are often less likely to support a candidate when the endorsement comes from an entity on a different end of the political spectrum.

Could Angus be Oprah?

In 1998, King took a side in a special referendum election asking voters whether they favored repealing a newly passed law banning discrimination based on sexual orientation. The first-term governor appeared in TV ads opposing the repeal of the law, which King had signed.

When the repeal prevailed, the result of high turnout among those motivated to stop the new law, repeal supporters singled out King for his defense of the law — signaling King’s endorsement in the race could have been key in motivating those who disagreed with the governor and resented his involvement in the campaign.

This year, King’s endorsement of Cutler — at least in one regard — fits the profile of an endorsement that could have a mostly positive effect on voter attitudes. King is among Maine’s most popular politicians. He enjoys substantially greater approval than disapproval for his performance in the U.S. Senate. That could mean fewer voters — especially those whose votes are in play — take King’s endorsement as a signal to oppose Cutler.

But Maine’s three-way race for governor this year doesn’t fit the profile of a race in which an endorsement would have a major impact. The race is anything but a low-information affair in which voters are searching for cues to determine the candidate who most closely matches their ideology.

Plus, King’s endorsement isn’t surprising. His nod to Cutler four years ago was surprising, since King hadn’t previously endorsed in gubernatorial races since leaving office. In 2008, Oprah’s backing of Obama was surprising because she never before made a political endorsement.

Cutler needs a major development to propel him into more competitive territory against Democrat U.S. Rep. Mike Michaud and Republican Gov. Paul LePage, said Jeff Selinger, who teaches political science at Bowdoin College in Brunswick. But, “barring a really high-profile and surprising endorsement … we’re not going to see that.”